European doctor joined old ship and set off (6)
I believe the answer is:
embark
'set off' is the definition.
(I've seen this in another clue)
'european doctor joined old ship' is the wordplay.
'european' becomes 'E' (abbreviation e.g. EU).
'doctor' becomes 'mb' (Bachelor of Medicine, Medicinae Baccalaureus).
'joined' says to put letters next to each other.
'old ship' becomes 'ark' (as in Noah's ark).
'e'+'mb'+'ark'='EMBARK'
'and' acts as a link.
(Other definitions for embark that I've seen before include "Put to sea" , "Go aboard" , "Start" , "Join ship" , "Go on board ship or plane" .)